Which term of the AP:125,121,117,.. is the 1st negative term?
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Let x be the first negative term
a=125
d=121-125=4
n th term is a+(n-1)d
==> x <0
==> a+(n-1)d<0
==> 125-4n+4<0
==> 129<4n
==>The smallest possible value of n is 33
for which 132>129
Thus x is the 33rd term
a+(n-1)d
=125-4n+4
n=33
=129-132
=-3
Hence -3 is the first negative term.
Hope it helps
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